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Abstract
The structural and polar nanoclusters have been found and studied out in model ferroelastics—mixed Hg 2 (Br,I) 2 crystals that were comprehensive investigated. The structural clusters are the nuclei of the low-temperature orthorhombic phase in the high-temperature tetragonal matrix, observed in a diffuse X-ray scattering at X-points of a Brillouin zone. They are related to phase transition and induced by fluctuations of an order parameter. The polar clusters, found out as quasi-local vibrations in a low temperature Raman-spectra, are due to disorder in an anionic sublattice and are induced by the polar mixed Br-Hg-Hg-I molecules and their proximate environment, which form ferroelectric and antiferroelectric nanoclusters.
Acknowledgments
The authors are indebted to A. A. Kaplyanskii for fruitful discussions. This study was supported by the Russian Foundation for Basic Research (project No. 05-08-33431) and the Program of Presidium of RAS (P-03).